1. Field of the Invention
The present invention relates to a method and an apparatus for recording image information on recording media such as disks by means of compression and encoding and to a method and an apparatus for reproducing the same.
2. Description of Related Art
Generally, data of image information is compressed and recorded on recording media such as disks, tape, and semiconductor memory in order to write as long a period of image information in an area having a limited size.
Conventionally, there has been widely used an MPEG (Moving Picture Experts Group) compliant compression encoding system as a data compression method.
The MPEG system processes image information by means of: predictive coding using the correlation of information about an image frame (or an image field) as a decoding and reproducing unit of the image information; and data compression using DCT (Discrete Cosine Transform).
The MPEG system categorizes images in each frame or field into three types, i.e., I, P, and B pictures according to compression encoding differences. For the ease of description, only the term “frame” will be used in the description below.
The I picture is also referred to as an in-frame encoding image subject to closed compression encoding within one frame only. The P picture is also referred to as a forward predictive encoding image subject to compression encoding by using the correlation with an image frame precedent to the image frame concerned. The B picture is also referred to as a bidirectional predictive encoding image subject to compression encoding by using the correlation with image frames precedent to and subsequent to the image frame concerned.
The MPEG system uses a so-called GOP (Group of Picture) comprising a plurality of frames (e.g., 15 frames) as a unit (read/write unit) of reading and writing to recording media. FIG. 15 shows an example of GOP.
As shown in FIG. 15, the MPEG system configures the GOP to always contain at least one I picture. This is because the use of only P and B pictures cannot decode images. Since the GOP contains the I picture, a random access is made possible in units of GOPS.
The I and P pictures are encoded in the same sequence as that of original images. The B picture is encoded after the I and B pictures are encoded. In consideration for the encoding sequence, an MPEG encoder resequences images from an original sequence in FIG. 15A to a sequence in FIG. 15B. The compression encoding is applied to the resequenced image information as described in patent document 1 (see JP-A No. 214265/1996).
As indicated with arrows in FIG. 15A, the P picture is subject to the predictive encoding by using a preceding I or P picture. The B pictures are subject to the predictive encoding in units of two B pictures sandwiched between preceding and succeeding I or P pictures by using these I or P pictures.
In this manner, the B picture uses succeeding I or P pictures for encoding. As shown in FIG. 15B, the B picture is resequenced so that it follows the succeeding I or P picture to be used for the predictive encoding.
As will be discussed below, the compressed and encoded image data is provided with management information for decoding and reproduction on the basis of a decoding and reproducing unit, namely, picture-based data, and is recorded on a recording medium. During reproduction of the image data compressed in the MPEG system, the management information for decoding and reproduction is extracted from the recorded data. Based on the management information, control is provided to output the reproduced image data in units of pictures. The sequence of pictures is restored to the original sequence.
When a digital camera is used to capture a still picture, for example, it is a conventional practice to superimpose information such as the capturing date and time on a recorded image. Further, for example, patent document 2 (JP-A No. 69995/1997) discloses the method of recording camera setup data separably from image signals.
The above-mentioned patent documents are listed below.
[Patent document 1] JP-A No. 214265/1996
[Patent document 2] JP-A No. 69995/1997
Many digital cameras can capture not only still pictures, but also motion pictures. Normally, the above-mentioned MPEG system is used to compress image data of motion pictures.
When the digital camera is used to capture motion pictures, it is convenient to be able to record information such as the capturing date and time and capturing conditions such as diaphragm adjustment, exposure values, white balance states, and focal lengths on a recording medium in addition to the image information. Such additional information can be used as management information about captured images.
The above-mentioned MPEG system can synchronize and multiplex image data and audio data to produce an encoded stream. There is known the MPEG-PS (PS for Program Stream), one of system formats for recording such stream on a recording medium. However, the MPEG-PS does not define how to multiplex the above-mentioned additional information such as capturing information on streams.
It has become a technical problem how to provide the additional information to a transmission format of data recorded in the MPEG system for convenient use.
In this case, it is intended to be able to easily retrieve targeted image information points or editing points. For this purpose, it is important to make it possible to use the additional information during variable speed reproduction that reproduces image data from a recording medium faster than a normal speed.